File permissions

Related terms

• Inode — The filesystem record that holds a file's metadata (owner, mode, size, link count) and where its data lives. A name in a directory just points to an inode number.
• umask — A per-process mask of permission bits that are removed from the mode of newly created files and directories. With 022, a new file gets 644 and a directory 755.
• setuid and setgid — Mode bits that make an executable run with its owner's (or group's) identity instead of the caller's; on a directory, setgid makes new files inherit its group. They show as s in ls -l.

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